Effect Of Carbon Nanotubes And Si₃N₄ Whiskers On Microstructure And Properties Of Mo₂FeB₂-based Cermets

Mo₂FeB₂-based cermets has high hardness,as well as wear resistance,corrosion resistance,high temperature resistance and fatigue resistance,and has good metallurgical bonding property with steel.It is a new type of hard material with low preparation cost and wide application prospect.However,Mo₂FeB₂-based cermet materials generally have problems such as high brittleness and low toughness in the current industrial production and use,which restricts the promotion and application of materials.Therefore,it is of great significance to study the strengthening and toughening of Mo₂FeB₂-based cermets.In this investigation,Mo₂FeB₂-based cermets were prepared by in-situ reactive vacuum liquid phase sintering method.The effects of nickel-plated and non-nickel-plated carbon nanotubes and silicon nitride whiskers on the structure and mechanical properties of Mo₂FeB₂-based cermets were investigated by scanning electron microscopy?SEM?,energy dispersive spectrometry?EDS?and X-ray diffraction?XRD?.Firstly,the surface of carbon nanotubes and silicon nitride whiskers was modified by nickel plating to prepare Ni-CNTs/Ni-Si₃N₄.The prepared materials were tested by SEM and EDS.The results show that the surface of the carbon nanotubes and the silicon nitride whiskers after the pretreatment were successfully coated with a beaded Ni-P composite coating by electroless nickel plating.Secondly,the effects of nickel-plated and un-nickel-plated carbon nanotubes on the microstructure and mechanical properties of Mo₂FeB₂-based cermets were investigated.The results show that when the addition amount of nickel-plated carbon nanotubes is0.5wt%,the mechanical properties are the best,and the hardness,flexural strength and fracture toughness reach the maximum values of 1228.4 HV0.3,1267.3 MPa and15.9MPa·m^1/2,respectively.Compared with the Mo₂FeB₂-based cermets added with un-nickel-plated carbon nanotubes,the comprehensive mechanical properties of the Mo₂FeB₂-based cermet added with nickel-plated carbon nanotubes are better and the improving effect is more obvious.The fracture path and fracture morphology of Mo₂FeB₂-based cermets with different amounts of carbon nanotubes are analyzed.The main toughenig mechanisms are crack deflection toughening,bridge toughening,toughening.Finally,the effects of different content of nickel-plated Si₃N₄ whiskers and un-nickel-plated Si₃N₄ whiskers on the microstructure and mechanical properties of Mo₂FeB₂-based cermets were investigated.The results show that when the addition amount of nickel-plated Si₃N₄ whiskers is 0.5wt%,the mechanical properties are the best,and the hardness,flexural strength and fracture toughness reach the maximum values of1196.8 HV0.3,1212.8 MPa and 14.58 MPa·m^1/2,respectively.On the other hand,the mechanical properties of Mo₂FeB₂-based cermets with nickel-plated Si₃N₄ whiskers are superior to those of Mo₂FeB₂-based cermets with unplated Si₃N₄ whiskers.As a reinforcing phase,Si₃N₄ whisker disperses in the matrix of Mo₂FeB₂-based cermet,which plays a good connection role and prevents crack propagation.The toughness of Mo₂FeB₂-based cermets is improved by the mechanisms of whisker pull-out toughening,crack deflection toughening and crack bridging toughening.